Screened-space-charge transferred-electron oscillators

We describe a novel form of a monolithic semiconductor oscillator in which the space-charge field of a drifting charge packet is modified, by means of the electrostatic boundary conditions of the device, so as to produce no voltage drop across the packet. Under these conditions, we predict that a sequence of narrow, identical, contiguous packets can be formed producing extremely high-frequency oscillations in the 30-300-GHz range, independent of the length of the drift region. This is in contrast to conventional transferred-electron oscillators in which the space-charge-induced voltage drop across either an accumulation region or a dipolar domain limits the drift region to, at most, a single packet at any time, thereby limiting the frequency achievable to packet-transit, -formation, or -decay times. Computer simulations and analytical solutions indicate that the frequency can be tuned electronically over a broad band by controlling the charge-injection level, while the oscillator center frequency depends upon the specific device geometry and the electron transport properties at the applied field. In theory, oscillations as high as 2 THz are not inconceivable.